Yes, you can change those Chinese tubes with some NOS tubes:
6P3P can be directly changed to 6L6, 6L6GC or 5881
6J8P can be directly changed to 6SJ7 in glass or metal cover
For the recitifier, can use 5Z4P, 5U4G, U52, 5R4G, 5AR4, GZ34, 5Y3......